1. Field of the Invention
The invention relates to Graphics Interchange Format Image (GIF) images, and more particularly to a method of converting a video file to become an animated GIF image in which consecutive frames of the GIF image share a same palette table for reducing the size of the GIF image.
2. Description of the Prior Art
Graphics Interchange Format Image (GIF) images have been used ever since 1987, and have been widely used on the World Wide Web since that time. GIFs are popular due to their properties of being able to use transparent backgrounds as well as for their animation effects.
An animated GIF contains two or more frames that are displayed in succession. A time delay can be specified between successive frames, and viewing the succession of frames can give the appearance of the image being animated.
The GIF format supports up to 8 bits per pixel, meaning that a single image can use a palette table that defines up to 256 colors. In an animated GIF, the same palette table can be shared for each frame within the animated GIF image, and this palette table will be referred to as a global palette. On the other hand, each frame can also be designed to have its own palette table that is not shared with other frames within the animated GIF image, and this palette table will be referred to as a local palette. Both global palettes and local palettes have their own advantages and disadvantages. Using local palettes allows the animated GIF image to have a greater number of colors since each frame can have its own color set, which improves the image quality over animated GIF images that use a global palette. In contrast, using a global palette reduces the file size of the GIF image by eliminating the need to use a separate palette for each frame of the GIF image. Having a reduced file size allows animated GIF images using global palettes to be downloaded faster than comparable animated GIF images using local palettes.
However, there exists a need for animated GIF images having improved color as compared to GIFs using global palettes and reduced file size as compared to GIFs using local palettes. Therefore, the conventional palette structure is need of modification.